I want to read this kind of diagram, but I haven't found the name of this, or somewhere I can find a legend of symbols used, or a tutorial to learn reading this...

I've googled this for over an hour, with similar images. Nothing :/

1st diagram


  • $\begingroup$ $\boxplus$ is modulo addition, $\oplus$ is the x-or, and $\lll$ is left rotate... If your read the papers, they mention those... $\endgroup$
    – kelalaka
    Jun 13, 2022 at 20:51
  • $\begingroup$ Depending on whether you look at a mathematical representation or pure computer code, $\land$ is either AND or XOR (C/C++/Java etc.). $\endgroup$
    – Paul Uszak
    Jun 14, 2022 at 0:36
  • 1
    $\begingroup$ @PaulUszak $\land$ and ^ are different. The former exclusively means AND. If you're using ASCII, then you'd want to use & for AND, | for OR, and ^ for XOR. If using logical symbols, you can use $\land$, $\lor$, and $\oplus$. $\endgroup$
    – forest
    Jun 14, 2022 at 0:39
  • $\begingroup$ @forest Well done. $\endgroup$
    – Paul Uszak
    Jun 14, 2022 at 0:40

1 Answer 1


These are fairly standard. $\boxplus$ is modular addition, $\oplus$ is XOR, $\lll$ is left rotate, and $\ll$ is left shift. Others you may see include $\land$ (logical AND) and $\lor$ (logical OR), as well as $\otimes$ (meanings differ).

For example, the second image you posted is the half round function of RC5. It is read as:

\begin{align} A &= ((A \oplus B) \lll B) + S_{2i} \\ B &= ((B \oplus A) \lll A) + S_{2i+1} \end{align}

Note that $S_{2i}$ and $S_{2i+1}$ are not labeled (they just come in at the left in your diagram and are indices into state array $S$), and the top left and right inputs and bottom left and right outputs are $A$ and $B$.

I ran the reference implementation for RC5-32/12/16 with a null key. In the first round:

\begin{align} A &= ((\texttt{0x9BBBD8C8} \oplus \texttt{0x1A37F7FB} \lll \texttt{0x1A37F7FB}) + \texttt{0x46F8E8C5}\\ B &= ((\texttt{0x1A37F7FB} \oplus \texttt{0x9BBBD8C8} \lll \texttt{0xE3054A3E}) + \texttt{0x460C6085} \end{align}

This results in $\texttt{0xE3054A3E}$ for $A$ and $\texttt{0xC4590FF6}$ for $B$.


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